1. Field of the Invention
The present invention relates to improvement of a lead acid battery.
2. Description of the Related Art
In a conventional liquid lead acid battery, a lead-antimony alloy grid is used as a positive electrode grid. If antimony is contained in a positive plate, however, antimony is eluted from a positive electrode grid body during charge/discharge operation. The eluted antimony moves in electrolyte, and precipitates on a negative plate to thereby reduce hydrogen overvoltage. Accordingly, the yield of hydrogen due to water decomposition increases, so that the water loss characteristic is lowered. Therefore, in some lead acid batteries, a lead-calcium alloy is used for a grid body. However, when charge and discharge cycles including deep discharge are performed with a lead-calcium alloy, a lead sulfate which is a dense insulator is generated in the interface between the grid and active materials during discharge, so that the capacity is reduced in early stages, or the connection among lead dioxide particles which are active materials is reduced, so that the active materials become easy to come off. In addition, in comparison with a lead-antimony alloy, a lead-calcium alloy is so soft that shortcircuit may be caused easily by extension of the grid.
If antimony is added to the positive plate, the connection strength among lead dioxide particles is increased. Therefore, there is no fear of reduction of the capacity in early stages or coming-off of the active materials. Further, if a lead-antimony alloy is used for the positive grid body, a corrosion layer generated in the interface between the grid and the active materials is made porous, and shortcircuit due to extension of the grid is hardly generated.
In addition, a retainer type battery which is one of valve-regulated lead acid batteries of such a type that oxygen gas generated during charge is absorbed in a negative electrode is configured such that a mat-like separator made from fine fibers (for example, a glass separator) is inserted between a positive plate and a negative plate for retaining sulfuric acid electrolyte required for discharge, and for separating both electrodes from each other.
If antimony is added to a positive plate, the hydrogen overvoltage of a negative plate is reduced by the same reason as mentioned above, so that the yield of hydrogen by water decomposition increases. As a result, fatal dry-up occurs to make the battery dead. Therefore, in the conventional retainer valve-regulated lead acid battery, a lead-calcium alloy is used for the positive electrode grid, and antimony is not contained in the positive plate.
Therefore, a lead-calcium alloy is used for a grid body in retainer batteries. However, for the same reason as mentioned above, in such retainer batteries, there are problems that the cycle endurance is short, and shortcircuit is caused easily.
If antimony is added to a positive plate, for example, by using a lead-antimony alloy for the positive electrode grid, and if antimony can be prevented from moving from the positive electrode to the negative electrode, it is possible to manufacture lead acid batteries superior in the cycle life performance.
It is an object of the present invention to provide a lead acid battery which is superior in the charge and discharge cycle endurance.
According to a first aspect of the present invention, antimony is contained in a positive plate, and an organic matter capable of capturing metal ions is contained in a separator between the positive plate and a negative plate.
According to a second aspect of the present invention, in the lead acid battery according to the first aspect, the organic compound is lignin.
According to a third aspect of the present invention, in the lead acid battery according to the second aspect, the lignin contained in the separator is thiolignin.
According to a fourth aspect of the present invention, in the lead acid battery according to the second aspect, the average particle size of the lignin contained in the separator is not larger than 10 xcexcm according to SEM observation. Further, the particle size of the lignin contained in the separator is not less than 0.05 xcexcm. Such a small particle lignin having a particle size less than 0.05 xcexcm is difficult to manufacture and is hard to be held by a separator. Accordingly, such a small particle lignin is not applied for a practical use.
According to a fifth aspect of the present invention, in the lead acid battery according to the second aspect, the BET specific surface of the lignin contained in the separator is not smaller than 2.5 m2/g. In this case, the BET specific surface of the lignin contained in the separator is not larger than 500 m2/g.
According to a sixth aspect of the present invention, in the lead acid battery according to the second aspect, the lignin contained in the separator is contained in a condition that the lignin is carried by granular silica.
According to a seventh aspect of the present invention, in the lead acid battery according to the first aspect, the lead acid battery is a retainer-type valve-regulated lead acid battery in which electrolyte is held in a mat-like separator, and oxygen gas generated in a positive electrode during charging is absorbed in a negative electrode; and antimony in a range of 50 ppm to 8,000 ppm is contained in the positive plate.
According to an eighth aspect of the present invention, in the lead acid battery according to the seventh aspect, antimony in a range of from 0.5% to 1.7% is contained in a positive electrode grid alloy.
According to a ninth aspect of the present invention, in the lead acid battery according to the seventh aspect, the separator has a multi-layer structure of not less than two layers, lignin is contained in at least one of the separator layers which are not in contact with the positive plate, the lignin content in the at least one separator layer being largest among the lignin contents in all the separator layers.
According to a tenth aspect of the present invention, in the lead acid battery according to the ninth aspect, the lignin content in the separator layer which is not in contact with the positive plate or a negative plate is largest among the lignin contents in all the separator layers.
Since antimony is contained in the positive plate, it is possible to prevent early-stage capacity reduction of the positive plate, coming-off of the active materials, and extension of the grid. If the material for capturing antimony ions is contained in a separator layer between the positive and negative plates, antimony can be captured in the separator layer. Therefore the increase of water decomposition can be prevented as mentioned above. Accordingly, features of maintenance free and water supply free can be given to the battery in the same manner as a lead acid battery containing no antimony in a positive plate. It was found that there was a large effect to prevent antimony from moving from the positive electrode to the negative electrode when lignin was contained, as the antimony ion capturing materials, between the positive and negative electrodes. In addition, it was found that a larger effect to capture antimony ions could be obtained when the contained lignin was, for example, made fine in its particle size, or carried by granular silica, so that the specific surface was made larger. Further, if the separator between the positive and negative electrodes is designed to have a multi-layer structure of two or more layers and if one of the separator layers which is in contact with the positive plate contains lignin the content of which is smaller than that in other separator layers, it is possible to restrain a bad influence due to decomposition of lignin in the positive plate during charging the battery. In addition, if the content of lignin in the separator layer which is in contact with the negative plate is made smaller than that in other separator layers, it is possible to restrain a bad influence such as deterioration of charge acceptance of the negative plate due to an excessive amount of lignin around the negative plate.